1. Field of the Invention
The present invention relates to a projection type display apparatus, and more particularly to an illumination optical system that guides light emitted from a light source to an image forming device.
2. Description of the Related Art
In a projection type display apparatus that magnifies and projects image light (picture image) formed by an image forming device such as a liquid crystal panel or DMD (Digital Micro-mirror Device), light emitted from a light source is guided to the image forming device by an illumination optical system. A typical illumination optical system has an integrator that uniformizes luminance distribution of light emitted from the light source, and a relay optical system guiding light outputted from the integrator to the image forming device. Further, between the light source and integrator, there is arranged a color separation unit such as a color wheel, if necessary.
In general, the integrator is roughly classified into “rod type integrator” and “array type integrator”. In the rod type integrator, light entering from one end is propagated to the other end while being reflected several times in the interior thereof, whereby the luminance distribution is uniformized. The rod type integrator is further classified into hollow column-shaped “light tunnel” and solid column-shaped “rod integrator”. On the other hand, in the array type integrator, light flux is separated and combined by a lens array having a plurality of lenses arranged in a matrix shape, whereby the luminance distribution is uniformized. In this specification, unless particularly specified, the rod type integrator (light tunnel or rod integrator) and array type integrator are referred to collectively as an “integrator”.
Here, in order to prevent lowering of image brightness, occurrence of shadow in an image, or the like, the image formation area (effective area) of the image forming device must accurately coincide with the irradiation area (illumination area) of illumination light in the image forming device. However, even when at the design stage, the effective area accurately coincide with the illumination area, the areas may not coincide in the actual fabrication. The chief cause for the difference is variations between constituent elements. For example, when there are variations of size, shape, optical characteristics or the like between optical elements constituting the integrator or relay optical system, even if these are arranged according to the design values, a difference between the effective area and illumination area occurs. Also, even when there is no variation of size or the like of the integrator or optical element, if positioning accuracy is low when these are arranged, a difference between the effective area and illumination area also occurs. Consequently, in fabricating the illumination optical system, position adjustment (fine adjustment) between the effective area and illumination area must be made as required.
As a method of making position adjustment between the effective area and the illumination area, there is a method in which the outlet end of the integrator is displaced. As another method thereof, there is a method in which a mirror disposed in an optical path of illumination light between the integrator and the image forming device is displaced.
Also, when a reflection type image forming device such as DMD is used, since illumination light must enter the image forming device from an oblique direction, the illumination area is distorted to a substantially trapezoidal shape. This is a phenomenon similar to a case where, when an image is projected on a screen from an oblique direction, the projected image is distorted to a substantially trapezoidal shape. Thus, Japanese Patent Laid-Open No. 2004-45718 has disclosed a technique for correcting the trapezoidal distortion (keystone distortion) by use of an optical system disposed between the integrator and image forming device.
Japanese Patent Laid-Open No. 2005-70271 has disclosed a technique for arranging on the outlet end face of a rod integrator an opening member that includes a reflection area around the opening area and for changing the opening member according to the size of image forming device to thereby adjust the size of illumination area.
The above method of making a position adjustment between the effective area of an image forming device and the illumination area of illumination light in the image forming device involves the following problem. First, when the outlet end of the integrator is displaced, the input end of the integrator is also displaced simultaneously; and thus there occurs a difference between the optical axis of light incident on integrator and the optical axis of the integrator. When the difference between the optical axis of incident light and the optical axis of integrator occurs, projected image luminance irregularity occurs.
Also, when the mirror disposed in the optical path of illumination light is displaced, unless the mirror is made to rotate around the light flux irradiated on the mirror, the optical path length of illumination light varies; when the optical path length of illumination light varies, the convergence point of illumination light moves forward of, or backward of the surface of image forming device, and thus the peripheral part of the projected image is darkened.
Further, according to the technique disclosed by Japanese Patent Laid-Open No. 2005-70271, while the size of illumination area can be varied, position adjustment between the effective area and illumination area cannot be made.